What regs revisions mean for zero carbon

New Approved Documents on energy use, ventilation and overheating are intended to be stepping stones towards zero carbon buildings. Julie Godefroy highlights their impact and where regulatory improvements can be made

Shortly before Christmas, the government published a Building Regulations package, including the new Approved Documents L and F for new and existing buildings, and a new Approved Document O on overheating for new homes and other residential buildings.

The changes will come into force in June, and are meant to be stepping stones towards the 2025 Future Homes/Buildings Standard (FHS/FBS), when new buildings will not need future retrofit to become zero carbon with grid decarbonisation.

Carbon reduction
The government expects this revision to deliver carbon savings of 31% for new homes and 27% for new non-domestic buildings. What it will actually deliver is uncertain, as the calculation methodologies (SAP and the NCM) do not relate well to actual performance, and cover regulated uses only.

The notional dwelling has a gas boiler; a heat pump would have given a clearer message

A major change is the introduction of a primary energy metric, alongside carbon dioxide, to encourage efficient use of energy resources at the system level. While no metric is perfect, 80% of consultation respondents, including CIBSE, raised concerns about this change because:

  • It means little to consumers, so doesn’t facilitate a closer link between performance and occupants
  • Primary energy and carbon emissions rely on conversion factors that change over time, so it doesn’t help with tracking progress
  • Primary energy could favour gas over electricity, which will send confusing messages on heat decarbonisation. An energy-use metric, together with carbon emissions, would better address the key goals of energy efficiency, carbon reduction and consumer engagement.

Low carbon heat
Gas connections to new buildings are still allowed, but will be banned from 2025 for homes and possibly some non-domestic buildings. The consultations included clear statements about heat decarbonisation, anticipating a mix of technologies in future, with a key role for heat pumps.

For new homes, the 2021 notional dwelling – the one that sets targets for the actual dwelling – has a gas boiler; a heat pump would have given a clearer message and more incentive for low carbon heat.

For non-domestic buildings, the heating fuel in the notional building follows that of the actual building, except for coal and other high-carbon fuels, which are compared with gas. A statement in the consultation response is a telling illustration of the perverse effects of these shifting targets: ‘We will be revising the specification of the heat pump notional building. This reduces the assumed efficiency of the heating system in the target building, providing additional incentive to install heat pumps.’1

Instead of setting an ambitious target that buildings would have to meet regardless of their heating system, promoting energy efficiency and low carbon heat in a technology agnostic way, low carbon heat is encouraged by allowing poorer installations, at the cost of performance and impacts on consumers.

There are important changes in how heat networks are treated:

  • For existing networks, the notional building is connected to a network of the same performance – so, there is no incentive for existing networks to improve. Instead, existing networks should be required to produce a decarbonisation plan, and their performance should be assessed on a much similar basis to other solutions.
  • For new networks, homes are compared with an onsite gas boiler, and non-domestic buildings with a network with 15% distribution losses supplied, for the majority, by a CHP, with some heat pump contribution, giving a carbon content of heat similar to that of an onsite boiler (0.23kgCO2/kWh). This should provide more incentive for efficient and lower carbon new networks.

New home
Significant changes are introduced to air permeability testing: all homes need to be tested, with sample testing no longer allowed. The low-pressure pulse (‘pulse’) technique, which provides results at 4Pa, is approved as an alternative to the fan pressurisation (‘blower door’) technique. Testing should be done according to CIBSE TM23 (2022).

Homes also have to meet the Fabric Energy Efficiency Standard. The maximum allowable air permeability is 8 m3/hr/m2 at 50Pa (vs 10 currently), or 1.57m 3/hr/m2 at 4Pa, and it remains 5m
3/hr/m2 at 50Pa in the notional dwelling. If the 2025 FHS is to meet its promise of ‘world leading’ standards of energy efficiency, this is an important area where improvements can still be found, along with MHVR for efficiency and air quality.

A new requirement has been introduced to limit overheating risk, which was widely supported by consultation respondents, including CIBSE. Compliance can be demonstrated through a simplified method in Approved Document O, or through CIBSE TM59 if more flexibility to the design and assessment is required.

Changes have been made to the simplified method to incorporate consultation comments – for example, on glazing areas’ size and orientation, and dwellings with communal heating. It is still difficult to gauge how well the method will work, so feedback will be important.

New non-domestic buildings
In addition to NCM compliance calculations, there is a welcome new requirement for non-domestic buildings of more than 1,000m2 (total useful floor area) to produce an energy forecast.

Unfortunately, the consultation proposals have been weakened significantly: the forecast can be done using TM54 (2022 revision), but also other options, including design calculations and benchmarks, both of which could mean anything. Some benchmarks are out of date, or don’t represent best practice.

At best, they represent a building type, while an energy performance model is specific to a building, guiding the design process and providing information to occupants on what the building could achieve and how to operate it.

AD-F introduces guidance that offices and other building types – such as gymnasiums, theatres or hotels – should have means of monitoring indoor air quality, typically through CO2 monitors.

This was initiated to reduce the risks of aerosol transmission of infections, but can be used to check that fresh air provision is adequate, and allow energy savings at times of low occupancy.

There are a number of small changes to the NCM, but government has acknowledged industry concerns and committed to a more fundamental review for the FBS.

Clearer guidance is given on commissioning. CIBSE had suggested introducing a penalty to Part L calculations unless evidence of commissioning was provided, as it cannot be assumed that systems will perform as efficiently as expected: this has not been adopted.

What you can do
CIBSE will provide more detailed information to industry, and comments to government, so do send us your feedback at JGodefroy@cibse.org. We are very interested in particular in the new overheating standard and simplified assessment method, as well as the revised SAP and SBEM and how they could be improved for the 2025 FHS/FBS.

Look out for a publication coming soon from CIBSE and LETI, on Net Zero definitions and accompanying FAQs.

1 SCOP of 264%, instead of 320% in the consultation

  • Dr Julie Godefroy is technical manager at CIBSE